> I'm a bit puzzled when someone makes a statement, as if there is a > "chemical" > difference between single weight and multiple viscosity oils. Yes, there is a chemical differecne... >If you lived in a desert climate as I > and some other list members, use of single 30 or 40W viscosity oil in the > summer is quite common due to the intense heat. The quality of the oil is the > same in both cases. It might be comon, but it is not optimum. The multi weight oil (especially a synthetic) will also give you much better viscocity index (VI) which is how well the oil maintains its viscosity at the extreme temperatures in the upper part of the cylinder bore. Its not necessary for one to use the best possible oil. But if you plan to keep your car indefinately, it will pay off in the long term. The lubricant technologies have improved, and it might make some sense for us to try to keep up with it. D^2